Methods for forming articles having decorative surfaces have been already described in the past. Within the last few years, a new decoration technique known as in-mold decoration (IMD) has gained acceptance and use in the molding industry and solves several of the problems associated with prior art techniques. See for example American U.S. Pat. Nos. 4,059,471; 4,650,533; 4,356,230 and 4,202,663. IMD combines the process of forming an article by injection molding with decoration of the article. In this method, a plastics carrier sheet, bearing a printed image, is placed in the cavity of an injection molding tool. Molten thermoplastic resin is then injected into the cavity to contact the carrier sheet. With suitable design of the injection molding tool, the pre-printed plastics carrier sheet becomes integral to the molded article or part. This is contrasted with the process described, for example, in European Patent application No. 799,681, where an image is transferred onto an article during the injection molding process. The molding process therein disclosed is a reaction injection molding, whereby reactive polymer components are injected into a mold at a relatively low temperature. The reactive components are mixed by injection and undergo a reaction, which raises the temperature of the mixture in the mold and produces hardened, cross-linked polymers.
The injection molding technique allows obtaining good results in terms of quality and precision also in case of decoration of articles having a complex shape. However, it has the disadvantage that it is very difficult and expensive to make modifications to the molds or any personalization to the printing process.
Another technique known in the art is the so-called thermoforming process, disclosed, for example, in the International Application No. 2004/067,599. It discloses flexible radiation curable compositions useful in thermoforming process which includes the steps of: 1) screen printing a polymeric sheet with a graphic design; 2) UV curing the printed ink; 3) thermoforming the printed sheets; 4) pressing the thermoformed sheet into a mold and applying vacuum; 5) cooling the product and removing it from the mold; 6) finishing the product to give it the final desired shape. The method therein described has the advantages to allow the ink to show good adhesion to the polymeric sheet, to avoid that prints stacked on top of each other stick to each other, to give the ink excellent flexibility and to allow successive interventions for aesthetical modification in the printing process. However, the decorated surface of the final product obtained by the method therein described has the disadvantage to show unpleasing cracks in the ink printed sheet, which aesthetically decrease its appearance for three-dimensional articles that include sharp angles. Additionally, the articles produced with the method disclosed in this international application, typically do not allow usage in exterior applications and in particular these articles do not satisfy stringent requirements that are imposed in the automotive industry.